The present invention relates to a method for filling particulate material into a tube. The method relates more particularly to filling a catalyst into a tube and then usually a whole series of vertical tubes, for example in connection with production of ammonia.
The main problem with filling particles into a tube is that voids easily form. This happens especially with particles which easily form bridges in the tube. To attain even filling, the tube can be vibrated, e.g. by tapping or striking the upper part of the tube. However, this is laborious and delays the filling operation. Furthermore, the tube is exposed to extra mechanical stress. When filling catalyst into the tubes, there is a special problem with unevenness because uneven filling and voids cause uneven temperature distribution over the tube. This creates temperature and mechanical stress in the tube and reduces its useful life.
A known way to reduce the above described problem is to first fill particles into a long sock or sock-like member, for example of soft plastic material. The particles or catalysts also can be delivered from the manufacturer in such socks. When filling the tubes, a sock with particles is fastened onto a line and lowered towards the bottom of each tube. By jerking the link, the sock opens below and the particles flow into the tube. Usually a large number of such socks is required to fill one catalyst tube. With this method, it is usual to tap the tubes to improve the degree of filling.
There are several disadvantages with this method. Particularly, if the sock contains voids among the particles, then one easily gets corresponding voids in the tube when the sock is emptied. Even and dense filling of the tube with particles consequently is difficult to achieve with this method. Different particle densities in the tubes cause variations in the pressure drop over the tubes. This results in distortions of gas distribution in a multi-tube reactor. The poor reproducibility with use of such filling operation means that the tubes must be exposed to extra tapping to secure reasonably even gas distribution over the tubes. In addition, the method is laborious. One is fettered to one packaging form and must often pay to get the particles filled into the socks. Systematic errors also may arise because of operator-dependent errors, both with filling the socks and with filling the tubes.
A special way to attain good and even packing of particles into a tube is to fill the tube with water and then to pour in the particles. However, this method requires that the water subsequently be completely removed. This removal and necessary subsequent drying takes a long time and to this must be added that not all types of particles/catalysts can endure exposure to water.
A method for filling a tube with a catalyst by adding the catalyst to the upper part of the tube by means of a transporter comprising a slowly rotating arrangement is known from RD Patent Application RD-253040-A. The catalyst is transported from a container through a duct in which there is a rod with oblique/transverse propeller wings or brushes. The catalyst particles are then transported to the upper end of the catalyst tube and fall smoothly into the tube. In order to get even filling of the tube, the particles must be added slowly. Further, the particles, especially during the first part of the filling operation, have a long drop and therefore may be crushed or broken during such fall. Consequently, one can get an uneven packing of particles over the vertical length of the tube. The filling time with this method also will be long.